The appeal of Hall Effect sensors

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Q. Why don't you use Hall Effect sensors instead of potentiometers, aren't they better?

A. This is something we're asked a fair bit via email. In theory a Hall Effect (HE) sensor should be better, but in practice it isn't such a clear cut decision. The answer basically has to do with them, for various reasons, not lasting as long. But even worse, we're leery of using them because of their failure mode. Take the last point; when a pot gets to be a problem it lets you know with increasingly poor centering. Usually this takes a while so you have plenty of warning. However, with an HE sensor, failure may be sudden - oops!

On the flip side, HE sensors are a 'lot' cheaper and price is a strong motivator toward everybody in the industry 'wanting' to use them. But let's turn this around and let's ask this; how would you (and modelers in general) view the trade off of 'us' saving 90¢ while increasing 'your' risk in the case of failure? And not just the risk of failure, but of sudden failure? I bet you'd take a dim view of it, right? This puts me in mind of my favorite Yogiism . . .



Finally, allow us a bit of salesmanship regarding ProModeler; with other brands if a pot goes south you have to send the servo in for service - you have no choice. Thing is, while replacing a potentiometer is an easy job because there are just three solder joints involved, by the time you get billed a 1/4 hour, plus the price of the part, as well as shipping both ways, the math doesn't work out. End result, you toss the servo. Thing is, because our customers are often not afraid of a soldering iron, you may be interested in knowing we offer parts for our servos. And not just the gears and the case like everybody else - but critically - we're happy to offer you just the potentiometer.


Let me tell you a story; back in the day it was routine to open your servos, remove a couple of small screws and access the inside of the pot. Then, using a cotton swap and alcohol you'd clean the carbon surface and the wiper tip to restore performance to like new. Presto you were good to go another year! Fast forward to today (+40 years) and the pots are sealed. They're also rated at a million cycles (not all, just the best ones like we use). But a million is not forever and thus, pots are actually a wear item. Of course the big guys know it. They could sell you just the pots - but they don't. Maybe it's because they know you'll buy another servo, instead (yes, I'm speculating).

Anyway, in this small way ProModeler is different; we're not run by the beancounters but by the engineers - and - we're modelers. The point being, we actually use our own product (in the trade it's known as eating your own dog food). Thus, you can take it to the bank we 'always' make decisions with respect to reliability, centering, response, and accuracy foremost in mind because we put our own models at risk - just like you.

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